|Subject:||[Libreboot] X60 tablet: screen whine after 1400x1050 screen swap|
|Date:||Mon, 6 Apr 2015 00:54:00 -0400|
If we compute the frequency as (0x61 << 8) + (0x61 << 6) + 1 (the 1 is to allow legacy backlight brightness which the VGA ROM allows and I don't know if it should be enabled) and duty cycle as (x << 8) + (x << 6) for x in 0xf, ..., 0x61, then both our issues are solved.
I don't know if the resulting value (0x79417940) gives low enough frequency to cause flickering for other users: "
I do not fully understand where or how the PWM frequency is set in src/northbridge/intel/i945/gma.c. I never see that 0x79417940 either. the only thing I see in http://review.coreboot.org/#/c/6731/7/src/northbridge/intel/i945/gma.c is:
write32(pmmio + BLC_PWM_CTL, 0x6100610);
In the source of my libreboot, it is still:
write32(pmmio + BLC_PWM_CTL, conf->gpu_backlight);
With src/mainboard/lenovo/x60/devicetree.cb setting it with:
register "gpu_backlight" = "0x879F879E"
Should it get changed to:
write32(pmmio + BLC_PWM_CTL, 0x79417940)
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